This project analyzes the role of neural networks in the cerebral cortex mediating the sensory function of the hand. It aims to understand how the hand acquires information through the sense of touch, and how sensory information about object size and shape guides the fingers in skilled tasks. The experiments investigate the neural mechanisms that mediate prehension: the ability to recognize and manipulate objects grasped in the hand. Neurophysiological recordings from single neurons and cortical ensembles in SI, SII and posterior parietal cortex measure the precise temporal relations between neural populations representing individual fingers at several stages of the cortical network to assess the functional significance of hierarchical and parallel processing. They evaluate the hypothesis that the brain uses sequential hierarchical and parallel distributed cortical networks in concert to compare the general features that classify an object grasped in the hand with its unique details. The experiments test important hypotheses concerning hand function: (1) Cortical representation of object size is an emergent property of hand use. (2) Population activity provides a better representation of object size and shape than the responses of individual neurons. (3) Tactile and proprioceptive inputs are bound together by synchrony of firing. (4) Hand movement enhances kinesthetic sensitivity. (5) Posterior parietal cortex encodes the spatial location of objects whereas the somatosensory areas of the lateral sulcus signal object form. Recordings made from populations of neurons distributed across the cerebral cortex will demonstrate how the brain integrates information from the fingers and from tactile and proprioceptive submodalities to form a unified percept of the grasped object. Synchronous measurement of the kinematics of hand movement and cortical electrophysiology will explain how the exploratory and manipulative procedures used to handle objects provide the sensory information necessary for fine motor control of the fingers and stereognostic appreciation of form. These studies will provide fundamental insights into the organization of cortical circuits, and the role of sequential hierarchical networks and parallel distributed processing in cortical function. The experimental paradigms will help define the neural basis of stereognosis, a major neurological test of hand function. They will provide novel and important neurophysiological data on sensorimotor integration in hand function, the tactile information processing capabilities of the cortex, the functional organization of different cytorarchitectural areas, and the temporal integration of spatial information within the cortex.